The production system of a developed hydrocarbon reservoir includes typically pipelines which combine the flow of several sources. These sources can be for example several wells or several producing zones or reservoir layers within a single well. To optimize production, it is often desirable to measure and monitor the inflow properties of each layer separately. The inflow properties include parameters such as the total liquid flow rate and static reservoir pressure.
Measurements of these properties have traditionally been performed using production logging tools such as Schlumberger's PLT™ disposed downhole on a cable (e.g., wireline, slickline) or other downhole conveyance tools.
Production logging is described in its various aspects in a large body of published literature and patents. The basic methods and tools used in production logging are described for example in the U.S. Pat. No. 3,905,226 to Nicholas and the U.S. Pat. No. 4,803,873 to Ehlig-Economides. Among the most advanced tools for production logging at present is the FlowScanner™ tool of Schlumberger.
By interpreting the results from production logging it is possible to determine the so-called Inflow Performance Relationships (IPRs), which give valuable information relating to formation pressure and near-wellbore formation damage (skin), optimal production pressures and flow rates, crossflow conditions and other important parameters. However in the presence of several formation layers or strata produced as comingled flow, comingling and crossflow between layers hinder conventional testing. In response to these difficulties, Selective Input Performance (SIP) testing has been developed.
In conventional SIP testing, production logging tools survey the well at different stabilized (pseudo-steady states) flow rates and at shut-in. An IPR curve is constructed for each layer by plotting pressure versus flow rate using data from two or more flow rates. These curves are then normalized to a reference hydrostatic pressure.
For further details on the measurement and known uses of inflow performance analysis, reference is made to U.S. Pat. No. 4,799,157 to Kucuk and Ayestaran, U.S. Pat. No. 4,803,873 to Ehlig-Economides, U.S. Pat. No. 7,089,167 to Poe and the Society of Petroleum Engineers (SPE) papers no. 10209, 20057, 48865 and 62917. Further reference to SIPs and their use can be found in the papers “Layered Reservoir Testing” by L. Ayestaran et al., in: The Technical Review 35, no. 4 (October 1987), 4-11 and “Production Logging for Reservoir Testing”, by P. Hegeman and J. Pelissier-Combescure in: The Oilfield Review, Summer 1997, 16-20.
It is further known that oil samples can be analyzed to determine the approximate composition thereof and, more particularly, to obtain a pattern that reflects the composition of a sample known in the art as fingerprinting. Such geochemical fingerprinting techniques have been used for allocating comingled production from multilayered reservoirs.
There are many known variants of the fingerprinting methods. Most of these variants are based on using a physico-chemical method such as gas chromatography (GC), mass spectroscopy or nuclear magnetic resonance or others in order to identify individual components of a complex hydrocarbon mixture and their relative mass. In some known applications, combinations of gas chromatograph and mass spectroscopy (GC-MS) are used to detect spectra characteristic of individual components of the complex hydrocarbon mixture.
Using a physico-chemical method, typically a limited number of selected components are identified and quantified for use as geomarker molecules. With one or a set of such geomarkers being characteristic of the flow produced from a single source or layer, it is possible to allocated the flow from that layer in the comingled total flow. Geochemical fingerprinting methods are for example described in U.S. Pat. No. 5,602,755A to Ashe et al. and in the published International Patent Application WO 2005075972. Further methods of using compositional analysis for the purpose of back allocating well production are described in the U.S. Pat. No. 6,944,563 to Melbø et al.
In the light of the known methods it is seen as an object of the present invention to provide a novel method of determining selective inflow performance curves for individual sources or layers in a subterranean reservoir and using the SIPs thus determined to establish important reservoir parameters.